Magnetic disk devices may employ magnetic heads larger in number than those required for ensuring a specification capacity, and the heads to be used may be selected, e.g., by a pre-shipment test. For manufacturing a magnetic disk device having a capacity, e.g., of 3 TB, ten magnetic heads and five magnetic disks are mounted on the magnetic disk device, and are adjusted to ensure a surface density per magnetic head equal to 334 GB in average. Nine magnetic heads required for ensuring the capacity of 3 TB are selected by successively selecting the magnetic heads satisfying the device specifications in descending order of capacity. The remaining one magnetic head is skip-processed as a skip head, and will no longer be used.